As compared with other preparing methods, solution-based synthesis for producing graphene oxide (GO) through chemical exfoliation from graphite has attracted considerable attention since the graphene oxide can be mass-produced with low manufacturing cost through a solution process. A GO-based flexible transparent conductive film has been studied a lot as a transparent electrode with potential applications as a thin film transistor, a sensor, or an organic photocell device. In general, the GO should be converted into reduced graphene oxide (rGO) in order to restore high conductivity of graphene. So far, there have been a lot of study reports showing various reduction processes. Geng et al. reported a simple method for preparing a transparent conductive graphene film by adjusting chemical reduction of exfoliated GO. Bao et al. reported that a post-annealing process at a high temperature (>800° C.) is needed to obtain rGO having an excellent electrical property. Although it was reported that a conventional thermal reduction process is more effective than a chemical reduction process, since most of the conventional methods are carried out at a high temperature for a long time, it is difficult to apply such methods to a flexible substrate such as plastic. Further, rGO has limitation such as a high surface resistance and a low uniformity, resulting in a low-grade electrical property. Therefore, an alternative GO reduction technique which can be applied to a flexible plastic substrate, and can be carried out rapidly and efficiently with high cost efficiency at a low temperature is still demanded for application of an rGO-based thin film. Meanwhile, Korean Patent Publication No. 2012-0008902 describes that a manufacture method of a partially reduced graphene film by heating and a manufacture method of a counter electrode of a dye-sensitized solar cell, but also has the above-described shortcoming.